1. Field of the Invention
The present invention relates generally to a model or toy autogyro that is flown from a tether and powered solely by autorotation of the autogyro rotor in response to wind forces, and in particular to a model autogyro of this type in which the rotor is attached in a manner permitting teetering of the rotor in response of changing wind forces, thereby providing lateral stability.
2. Description of the Prior Art
Tethered model or toy autogyros, are flown much like kites, with the autogyro being connected to the flyer by a string or tether. As used herein, the term "tethered autogyro" is intended to describe an autogyro flown on a line or tether, and not as a limitation requiring the tether to be attached. Like kites, autogyros are lifted into the air by the force of wind against a surface. In the case of autogyros, the wind acts against the lower surface of rotor blades, causing the blades to turn, creating lift on the autogyro.
Basically, autygyros are comprised of a fuselage, a rotor mast or shaft that extends upwardly from the shaft and a rotor that turns at the top of the mast. The tether is normally attached to the front of the fuselage at a point which causes the rotor to tilt rearwardly when the autogyro is airborne so that the wind will impact the underside of the rotor blades.
An autogyro rotor turns in response to the force of the wind against the underside of the rotor blades. On one side of the rotor, the blade approaches the wind, while the blade on the opposite of the rotor moves away from the wind. Lift on the blade moving toward the wind is greater than on the blade moving away from the wind due to the difference in the configuration of the blade leading and trailing edges, and to the greater relative velocity of the wind on the approaching blade. This greater lift tends to lift the approaching side of the autogyro more that the other side, causing the autogyro to turn or roll, instead of maintaining level steady flight.
Various proposals have been made in the prior art to address this problem. For example, U.S. Pat. No. 5,381,988 to Kattas describes an autogyro, or autoglider, in which the rotor is connected by a horizontal hinge to the top of a shaft that rotates in a bushing at the top of a vertical mast. In an autogyro described in U.S. Pat. No. 3,194,521 to Rider et al., the inner end of each rotor blade is hinged to a rotor hub that is mounted on a rotatable shaft. Each blade, as it is on the approach side of its rotation, is raised to compensate for the greater lift.
Model autogyros, to be flown successfully, must be light in weight. Since they often crash, they must also be durable. Since their lift depends upon the free rotation of the blades under, often gentle, wind forces, any friction that must be overcome limits the flying ability of the autogyro. Unfortunately, the above designs, due to their complexity significantly increase the autogyro's weight, and are easily broken. Moreover, the attachment of the rotor to a shaft that must be rotated in a bushing or housing produces frictional forces that restrict the turning freedom of the rotor.
An autogyro design addressing the problem of stability without adversely affecting the flying characteristics of the autogyro, or its durability, would be of considerable value and utility.